Drainage method for four-wire-cable systems



Sultana' a; tel' fatwa@ June A1, 1926.

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EALPE e. noounmr, or ENGLEWOOD, NEW JERSEY, assrGNon To AMERICAN TELE-r2 rnoNE Nn TEEEGEAPH COMPANY, .a coEPonA'rIoN or NEW YoEx.

DRAINAGE METHOD IOR FOUR-WIRE-CABL SYSTEMS. y

Application led October 7, 1925. .Serial No` 61,101..

This invention relates to transmission systems and more particularly to improvements 1n four-wire circuits 1n such ls stems 1n which .the conductors are groupe togetherV 5 in cables between stations.

Because of the close association and frequent twist of the conductors comprising the I pairs and quads which make up the cable, and because of the presence of the sheath,

lo noise due to direct capacitance unbalance and mutual inductance between ower circuits and telephone circuits in ca le is very small. Noise is, however, often introduced by voltages induced along the conductors which causes longitudinal currents and voltages between the various quads, between quads and sheath and between quads and ground at points where terminal equipment '1s connected. These longitudinal currents 'to and voltages cause noise through their action on the small unbalances of the circuits. These unbalances are of two general types, those due to dilerences-in the series impedance of the two sides of circuits and those 26 due to differences in the shunt admittances to other conductors to the sheath and to ground y in the case of central office equipment. Thepurpose of this invention is to provlde arrangements particularly adaptable for cir- 30 cuits of the well known four-wire type for materially decreasing the noise introduced on such circuits b conditions of unbalance. This reduction 1n noise is accomplished by novel methods of drainage vwhereby the drainage is applied -to the circuits at points therein where the volume or power level is tomparatively high, such as at the output of the four-wire repeaters. Other objects and features of the invention will appear more fully from the detailed description thereof hereinafter 'ven.

In cases where series unbalances are small and shunt unbalances are of considerable importance, reductions in noise may be obtained by drainage. By'drainage is meant connecting the wires of the circuit to ground in such a way that the average voltage to ground of the two sides of the circuit is greatly reduced without appreciably lowerlng the magnitudes of the useful voltages and currents of the circuit. On a telephone circuit this may be accomplished by connecting to ground the midpoint of a well balanced retardation coil or phantom coil whose Ater- 5 minals are connected across the circuit. If

accomplished througlh drainage, as the regreatest. 1n the general case, unbalances of both the series and shunt types are present so that little effect one way or the other is duction in effect of t e shunt unbalance ma be largely neutralized by' the increased e fect ofthe series unbalance.

Where four-wire circuits are involved, however, it is possible accordin to the methods and arrangemen of this invention to take advantage of the unilateral propagation characteristics and changes in the volume or power level along the circuits to obtain a-.beneficial effect from drain 'Ue so 50 as to materially reduce the noise intr uced y in the circuits." In a four-wire circuit it will be noted that near the repeater points, the volume or power level in the circuit transmitting in one direction is relatively high land in the other circuit transmitting in the opposite direction at the same point the volume 4ol power level is relatively low. Noise introduced on the circuit by rdrainage at a point where the volume orrpowcr level 00 is high will have a small ete'ct on the circuit as ,compiu'edv to asimilar noise introduced on 'the circuit where the volumeor power level is low. According] in accord-v ance with the arrangements o this inven- 9B tion, -drainage is accomplished by grounding the midpoints of the line sides of repeating coils on the phantoms on the output sides of the repeaters in cable' circuits of the four- A wire types. Accordingly noise caused by 1'00 the effect of shunt unbalance in the circuits may be eliminated yb the drainage method of this invention an at the same time the noise caused bythe effect of series unbalance will have a' small effect on the circuit. The v106 voltages to vground of the circuits transmitting in the opposite direction which are not drained, are greatly reduced through the shielding effect of the large number which are drained and the eiects of shunt unbal- 1l.

r B of hi h volume or gether with the accompanying drawing inv the Figures 1, 2, 3, 4 and 5 of which the invention is illustrated. Fig. 1 shows schematically a cable circuit between repeater stations. Figs. 2 and 3 show the arrangements of the quads in the cable at different points on the circuit. Fig. 4 is a diagram illustrating the volume or power level at dierent points on the circuits and Fig. 5 is a detailed circuit diagram of the circuit and drainage arrangements of the four-wire sys-l tem of the invention.

In Fig. 1 is shown a cable C interconnectin the repeater stations E and W. The ca le would be composed of ductors of which would make up the oneway circuits of a four-wire system. These conductors are shown in more detail in Fig. 5 in which circuits 10 and 11 would be oneway circuits transmitting from repeater E to repeater W. A phantom circuit 13 would also be composed by these two circuits. Circuits 8 and 9 would be one-way circuits transmitting from repeater W to re,- peater E A phantom circuit 12 would also be composed by these two circuits. The repeating coils, or transformers, whereby these circuits are connected to the4 inputs and outputs of the repeaters would be 4lo-y cated at approximately the points indicated in Fig. 1 by the dotted lines A, A and B, B, or in other words close tothe repeaters. As is well known the one-way circuits of fourwire system have the characteristic that the v volume or power level will fall 0H materially from a point close to the repeater output to another point near the successive repeater input. The volume or power drop on the circuits 10, 11 and 13 between points such as A, A, and B, B would e shown in Fig. 4 by the line E-VV. The volume or power drop on the circuits 8, 9 and 12 between oints B, B,

and A, A would be shown by t e line W-E.

Accordingly at these points A, A, and B, wer level the line side win ings 4 and 6-o the phantom circuit coils of the repeater outputs aredrained by means of the ground connections 5 and 7 respectively. This drainage will elilninate noise due to the eiect ofshunt unbalances,

and at the same time this may increase the noise due to the series unbalance, nevertheless it is pointed out that this' noise is introduced on the circuit at points such as A,

quads, the conmasses A, and B, B where the volume or power is at a relatively high level, and hence will have a relatively smaller effect than if introduced elsewhere. It is pointed out that the connection of the drainage to the midpoint of the phantom coil serves to drain y oth'side circuits as well as the phantom.

without any increase in their longitudinal currents. Hence the eiects of shunt unbalances on these pairs of conductors are reduced at a point where the power or volume level is low without any increase in the ef ects of their series imbalances. There is thusa considerable reduction obtained in the total noise on these circuits.

The beneficial effect of the drainage arrangements o this invention is most marked when the uads of the cable are arranged as shown inqFigs. 2, 3 and 5. As shown in these figures, the quads of the cablel are 'iti grouped for four-wire transmission by utilizing conductors in the outside layers for transmission in one direction and conductors in the inner layers for transmission in the o posite direction. At a point, such as 3 of dtig. 5, midway between repeater sta' tions, the two groups .changed and connections are made at the ends so that repeater outputs in all cases are connected to the circuits in the outer group and repeater inputs to circuits in the inner grou Cross-sections of the cable at points A, and B, B, illustrating this arrangement are shown in Figs. 2 and 3 respectively.

While the arran ements of the invention have been disclose as embodied in certain specific forms which are deemed desirable it is understood that the invention is capable of embodiment in many other widely va 1. In a four-wire transmission system two 'ff repeater stations interconnected by a cable circuit, said cable circuitcomprising a plurality of quads, a substantial number of said quads comprisin one-way side and phantom circuits of said our-wire system, and means in certain of said quads for grounding the midpoint or the line side of the phantom circuit repeating coil on the output sides of said repeaters.

2. In a four-wire transmission system two repeater stations interconnected by a cable circuit, said cable circuit comprising a plurality of quads, a substantial number of said quads comprising one-way circuits for transmission in the same direction over said four- 'of quads are inter-I [rage to the circuits of said quads' at points thereon where the volume or power `is relatively large.l

3.- In a.; four-wire transmission system comprising tworepeater. stations interconnectedby a cable circuit in which said cable circuit comprises a plurality of quads and a substantial number of saidv quads include oneway circuits for transmission in the seme direction over said four-wire system, the method of reducing noise on said circuits dueto the eect of shunt unbalances thereon l balances thereon which consists in introducing drainage on said circuits at oints thereon where the volume orpower evel is relatively large.

In testimony whereof, I have signed my 20 RALPHY G. MOCURDY. 

